Absorption in infrared spec help ?

Hi for this question, it asks to identify E and F. I understand that E is propan-2-ol and F is a propanone. But there is a small absorption at the 3000cm^-1. I know that F is definitely a ketone but how can you justify the small absorption at 3000-3500cm^-1?

Thanks

(edited 7 years ago)

My guess is that it's the C-H single bonds.

Reply 2

Pigster

20

Original post by Kvothe the Arcane

My guess is that it's the C-H single bonds.

your guess = correct

w00t

Reply 3

coconut64

OP

16

Original post by Pigster

your guess = correct

w00t

There are two absorptions though, are they both from the C-H bond? Thanks

Reply 4

alow

19

Original post by coconut64

There are two absorptions though, are they both from the C-H bond? Thanks

There's more than 2. Basically everything in that region is from X-H bonds, and you get a lot of peaks from vibrations associated with C-H bonds in organic molecules. That spectrum is very typical in the region around 3000 wavenumbers.

Reply 5

coconut64

OP

16

Original post by alow

There's more than 2. Basically everything in that region is from X-H bonds, and you get a lot of peaks from vibrations associated with C-H bonds in organic molecules. That spectrum is very typical in the region around 3000 wavenumbers.

So carboxylic acid absorption is always much lower and broader and more distinguishable than these kind of absorption ? How do you not mistake this absorpotion with the cooh or O-H absorption?

Thanks

Reply 6

MexicanKeith

12

Original post by coconut64

So carboxylic acid absorption is always much lower and broader and more distinguishable than these kind of absorption ? How do you not mistake this absorpotion with the cooh or O-H absorption?

Thanks

O-H is good at hydrogen bonding and is a very polar bond, these two factors lead to 2 common features of COOH and OH absorbtion bands:

1) they are broad- due to hydrogen bonding

2) they absorb very strongly -because they are polar (you don't need to worry about the reasons behind this

(edited 7 years ago)

Reply 7

coconut64

OP

16

Original post by MexicanKeith

O-H is good at hydrogen bonding and is a very polar bond, these two factors lead to 2 common features of COOH and OH absorbtion bands:

1) they are broad- due to hydrogen bonding

2) they absorb very strongly -because they are polar (you need to worry about the reasons behind this